I found a work around. Here:
https://unix.stackexchange.com/questions/329939/processing-paths-in-m3u-fileYou can set the Mac to run a shell script, either as a workflow or as an App or as a Folder Action or or as a Service or as a Script.
The Folder Actions function is spotty at best, so I'm using a script and FastScripts, a free app (for 2 scripts) that runs scripts.
The script I use is the following:
Open Apple Script Editor in Utilities Folder.
Type the following into the script editor:
set thePath to "Set/to/path/of/device"
do shell script "awk -F/ '!/^#/{$0=$NF}1' /Set/To/Path/of/device/Playlist.m3u > /Set/To/Path/of/device/testfile.tmp && mv /Set/To/Path/of/device/testfile.tmp /Set/To/Path/of/device/Playlist.m3u"
my settings are:
set thePath to "/Volumes/Walkman_SD/MUSIC/Podcasts/"
do shell script "awk -F/ '!/^#/{$0=$NF}1' /Volumes/Walkman_SD/MUSIC/Podcasts/Podcasts.m3u > /Volumes/Walkman_SD/MUSIC/Podcasts/testfile.tmp && mv /Volumes/Walkman_SD/MUSIC/Podcasts/testfile.tmp /Volumes/Walkman_SD/MUSIC/Podcasts/Podcasts.m3u"
Set to path is the playlist on your given device, which should be /Volumes/YourDevice/. I use a Sony Walkman nw-a35.
Save the script in your ~/Library/Scripts folder or /Library/Scripts/ folder if you want all users to access it. Then open up FastScripts and set the Script you save to a function button by clicking on "none" and pressing the function key you want to use. I use F14. Then when you save a playlist to your device, you can press F14 and the Playlist will automatically remove the path to the song files.
Or you could do a folder action or service (the services show up in the menubar of the Finder under the app name).
Open up Automator which is found in the Applications folder. Choose New Document and select (app, workflow, folder action) Service.
Then go to Utilities on the left (you have to scroll down a bit), and drag "Run Shell Script" to the area on the right. This should open up a balloon where you can type in code. Be sure to select "as arguments" from the drop down on the upper right corner of the balloon (the default is "to stdin".
then copy the following code into the dialog box:
awk -F/ '!/^#/{$0=$NF}1' /Set/To/Path/of/device/Playlist.m3u > /path/of/device/testfile.tmp && mv /path/of/device/testfile.tmp /Set/To/Path/of/device/Playlist.m3u
setting the path to your device's path (/Volumes/YourDevice/Path/to/playlist/folder)
then save and look in the services menu on the menu dropdown for the app's name in the upper left of the screen. That should show your script in the services menu.
Like I said, the Folder Actions is spotty lately, but you can try it by creating a Folder Action in Automator the same way as the Service, and right clicking on the folder of your playlist in the /Volumes/YourDevice/ folder, then selecting Folder Actions Setup. This will show you the option to add folder actions to that folder. For more info, lookup Folder Actions Setup in your favorite search engine.